The organic EL devices have been expected to be applied to color wide screen image display devices replacing liquid crystal display devices, and have been intensively developed. Recently, although displays using the organic EL devices have now been used in practical applications, full-color image display devices using the same are still in the course of development because they lack in sufficient light-emitting property. In order for improving the light-emitting property, very high-efficiency green organic light-emitting devices based on electrophosphorescence employing ortho metalized iridium complex (fac-tris(2-phenylpyridine) iridium) as a phosphorus light emitting material for the organic EL device are proposed. (refer to Non-patent literatures 1 and 2 below)
Because the current organic EL devices employing the phosphorus photoluminescence are limited to emitting only green light, coverage as the color display devices is narrow. Therefore, it has been demanded to develop organic EL devices which emit light of different colors from green with improved light emission property. Regarding particularly with EL devices which emit blue light, those having an external quantum yield exceeding 5% is not reported yet. Accordingly, an improvement in the EL devices which emit blue light, if possible, enables the display devices to display full colors or white light resultantly advancing toward practical use of phosphorus light EL device greatly.
Currently, developments about a compound having Ir atom as a phosphorus photoluminescence complex are actively carried out, and Compound A below is known as a material employable for an EL device which emits green light. On the other hand, Compound B below is known as a material for an EL device which emits blue light, however, the EL device employing Compound B is not practical in view points of both lifetime and efficiency of the device. Accordingly, it is necessary to develop another complex for EL devices which emit blue light, however, any material except Compound B has not been found yet now.

Although the above Compounds A and B are complexes having a bidentate chelate ligand, almost no complex having a tridentate chelate ligand similar to the above compounds is known except Compound C below. (refer to Non-patent literature 3 below)

However, Compound C serves to emit reddish light having light emission wavelength of around 600 nm, without capability of serving to emit bluish light. Accordingly a realization of a complex having a tridentate chelate ligand which serves to emit bluish light, if possible, has a possibility of new technology development.
Non-patent literature 1: D. F. O'Brien and M. A. Baldo et al. “Improved energy transfer in electrophosphorescent devices” Applied Physics letters Vol. 74 No. 3, pp 442-444, Jan. 18, 1999
Non-patent literature 2: M. A. Baldo et al. “Very high-efficiency green organic light-emitting devices based on electrophosphorescence” Applied Physics letters Vol. 75 No. 1, pp 4-6, Jul. 5, 1999
Non-patent literature 3: J-P. Collin et al, J. Am. Chem. Soc., 121,5009 (1999)